Probabilistic design life selection procedure for a steel bridge

Numerous bridges and viaducts built in Western Europe in the middle of the 20th century are now in service for more than 50 years. Aging and changes in societal demands result in a gradual decline of their technical and functional performance. This consequently forces responsible authorities to replace the obsolete infrastructure in the coming decades.

Large‐scale renovation programs together with further development of the highway network require a lot of resources and make a significant environmental impact. The assumed design life of bridges affects structural solutions and the choice of materials. Therefore, there is an opportunity for more efficient use of resources and reduction of the environmental impact if the design life of new bridges is optimized with respect to life cycle costs and CO₂ equivalent emissions.

As multiple design life options exist for any bridge, it is essential to have a consistent approach capable of indicating the favorable option. Therefore, a procedure has been developed for comparison of various design life options based on lifecycle costs and lifecycle CO₂ equivalent emissions. The procedure accounts for different traffic growth and traffic load development scenarios and it considers probabilities of these scenarios to happen in the future. This allows to assess the effect of uncertainty in functional parameters resulting in probabilistic lifecycle costs and emissions, which indicate a proper design life option.

The procedure is applied to a large span steel bridge over a river. Two design life alternatives, namely 100 years and 200 years, are considered. This paper summarizes the results of this study and it offers a discussion on limitations and perspectives of the suggested procedure.